A magnetorheological (“MR”) fluid is a fluid that can increase apparent viscosity when subject to a magnetic field. An MR fluid typically includes a suspension of small magnetizable particles (e.g., iron) in a carrier fluid (e.g., oil). In an inactive state, the MR fluid can have a viscosity similar to low viscosity oil. Upon application of a magnetic field, the viscosity of the MR fluid increases even to the point of becoming viscoelastic in some instances.
MR fluids can be used in various types of brakes, clutches, or actuators to provide variable resistance. Such MR devices typically have high torque-to-volume ratios, inherent stability, and simple interface between mechanical and electrical components. As a result, MR devices have been implemented in civil engineering, haptic technology, exercise equipment, automobile suspensions, tactile displays, and other technical areas.
MR devices, however, exhibit hysteresis in operation. For example, an input current can be initially applied to obtain a desired torque output from an MR device. However, after the input current is removed, the torque output of the MR device does not return to zero, but instead has a residual value. Such a behavior is commonly referred to as MR hysteresis. Conventional solutions to address MR hysteresis include generating mathematical models of particular types of actuator based on experimental data. These mathematical models require extensive experimental data, certain magnetic field assumptions, and inability to capture certain hysteresis behaviors.